You've just got a strap you're pulling it on-- so obviously there was a design defect.

只有一根带子让你拉着走-,很明显这是设计的缺陷。

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He had a suitcase that--I don't know exactly, something like this--had a strap that you'd pull it along and it had four little wheels on the bottom and it worked.

他的行李箱。。。我知道的不太确切，应该是这样的，那上面有一条带子,你可以拉着它,而箱子底部有四个小轮子可以使箱子滑动。

耶鲁公开课 - 金融市场课程节选